Layer 2 loop problem because of default vlan

Publication Date: 2014-04-29Views: 1013Downloads: 0

Issue Description

Even if you have STP or MSTP or SEP or RRPP inside your layer 2 network, managing faults is always challenging. Failures often transform to layer 2 loops which severely impacts the business. Some time ago I had an engineering case and I would like to share the story with you. So let’s start.
Working environment is very simple. We have a single RRPP ring deployed like below:

What do you think it will happen if we deploy this configuration? It will successfully break the loop and avoid any broadcast storm? Apparently this configuration will guaranty a loop free domain, but we didn’t consider one point.
VLAN 1, default vlan, is not protected. Even If we didn’t explicitly configured, as you can see below, VLAN 1 is contained by all interfaces, because is the default vlan, which cannot be deleted and does not need to be created.

In this situation, broadcast storm might occur on vlan1 causing equipments to overload and disrupt traffic on other vlans, including control-vlan 4091, so hello control packets will be loss and RRPP ring will become unstable. You don’t to experience this.